Fro

google

ref

Middle English: from Old Norse frá (see from).

wiktionary

ref

From Middle English fro, fra, from Old English fra(“from”), from Old Norse frá(“from”), from Proto-Germanic *fram(“from”), from Proto-Indo-European *promo-(“forth, forward”). Cognate with Scots frae(“fro, from”), Icelandic frá(“from”). More at from.

Clipping of afro.

etymonline

ref

fro (adv., prep.)

"away, backwards," c. 1200, Northern English and Scottish dialectal fra, Midlands dialect fro, from Old Norse fra "from," from Proto-Germanic *fra "forward, away from," from PIE *pro- (see pro-), extended form of root *per- (1) "forward," hence "in front of, before, toward, near," etc. The Norse word is equivalent to Old English fram, thus fro is a doublet of from.